284 THE CIRCULATION OF NITROGEN [PART III 



transmutations into higher forms of life — into other re-incarnations. 

 But the larger sea-weeds are not eaten to a great extent by 

 animals. Fishes, molluscs, and some other marine animals browse 

 upon them, and man does indeed eat certain succulent algae. But 

 the amount of the larger sea weeds thus disposed of is inconsider- 

 able and there is no doubt that an immense quantity of marine 

 algae, directly nourished upon the nitrogen washed down from the 

 land, is not utilised by animals but simply dies and putrefies, some- 

 times on a very large scale. On the shores of Belfast Lough, for 

 instance, there grow immense quantities of the sea-lettuce (Ulva 

 latissima), which are nourished upon the luxuriant food materials 

 afforded by the sewage of Belfast. Purification of this sewage by 

 the septic methods is quite useless, so far as the avoidance of the 

 nuisance is concerned, for the Ulva appears to prefer the nitrates 

 of the septic effluent to the organic matter or ammonia of the 

 crude sewage \ There are no animals which utilise the sea- weed 

 as food and the result is that great masses of the Ulva are simply 

 washed ashore to die and putrefy, becoming a serious nuisance, and 

 even a danger to health. 



Therefore when the nitrogenous drainage from the land is 

 utilised by the larger sea- weeds its further organic progress may be 

 interrupted, the element again passing into the inorganic phase. 

 So also with a certain proportion of the diatoms and other proto- 

 phyta which have utilised this dissolved food-stuff. There is no 

 doubt that vast quantities of these organisms must die and fall to 

 the sea bottom, there to putrefy. This must happen in the 

 Antarctic Ocean, where there is an immense accumulation of deep 

 sea ooze formed predominantly from the dead shells of diatoms. 

 We must remember that at the bottoms of deep seas the tempera- 

 ture of the water is verj^ low, and that bacterial action, and 

 therefore putrefaction, may proceed very slowly. It may be the 

 case then that a large proportion of the organic substance of the 

 diatoms falling to the sea bottom is utilised as food by the abyssal 

 animals living there. We must recognise however that some at 

 least of the organic plant substance built up from the nitrites and 

 nitrates washed down from the land, at once undergoes putrefaction, 



^ See Letts, loc. cit. 



